[LLVMdev] Broke my tail (call)

[Jon Harrop]

On Tuesday 24 February 2009 20:05:52 Dan Gohman wrote:
> "first-class" in this context means "Values can have this type", not
> "everything that anyone might want is supported in all backends."

Ok.

> A meta issue is that LLVM IR differs from many virtual machine ISAs in
> that it's more of a language for expressing programs than a
> specification of what some particular machine can actually execute.  When a
> particular LLVM component doesn't support a particular aspect of the
> language, it's considered a bug in the component, and not necessarily
> considered a problem in the language.

Right.

> This arrangement is convenient for people developing LLVM itself,
> because new language features can be added without the requirement
> that all backends and execution engines support all features in full
> generality, which isn't always immediately useful, and sometimes not
> even meaningful.  However, it's inconvenient for people using LLVM,
> because there's no complete list of which features are actually
> supported on any given backend.  Some features that are commonly
> unsupported are now mentioned LangRef.html, though it's certainly
> not complete.

I think it would be extremely useful to document what exactly does not work 
and where these unwanted interactions occur in way that makes it as easy as 
possible for people to reference, so they can forsee bumps before they start 
building upon anything.

I read other people's tales of woe with regard to some of LLVM's experimental 
features and learned to avoid them early on. This is one of the only minor 
niggles I've discovered myself. Once I have my own basic functionality up and 
running I'd like to move on to the more experimental stuff because it holds 
so much promise.

> One way this issue might be addressed is with an LLVM IR
> conformance test suite.  Covering the whole language would be a
> big project, but the work could be done incrementally.  I wonder if
> people would be interested in working on this.

I would value other work a lot more, such as filling out the C bindings.

> > Shall I file this as a bug against LLVM?
>
> Yes, thanks.

Will do.

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e